What is the Difference Between GFR and CrCl

The main difference between GFR and CRCL is that GFR is the flow rate of filtered fluid through the kidney whereas CrCl is the volume of blood plasma cleared of creatinine per unit time. Furthermore, CrCl is a useful measurement for approximating GFR.

GFR (glomerular filtration rate) and CrCl (creatinine clearance rate) are two measurements of the renal function. They are used to assess the excretory function of the kidney during the diagnosis of chronic kidney disease, albuminuria, and kidney diseases.

Key Areas Covered

1. What is GFR
     – Definition, Reference Values, Importance
2. What is CrCl
     – Definition, Reference Values, Importance
3. What are the Similarities Between GFR and CrCl
     – Outline of Common Features
4. What is the Difference Between GFR and CrCl
     – Comparison of Key Differences

Key Terms

Creatinine, CrCl, Chronic Kidney Disease, GFR, Renal Function

What is GFR

GFR (glomerular filtration rate) is the total filtration rate of a functioning nephron in the kidney. However, the GFR cannot be measured directly. Therefore, it has to be measured in terms of an ideal filtration marker such as insulin, iohexol or iothalamate. Generally, these are the Gold standard markers for the measurement of GFR. But due to the cumbersome procedures involved in the measurements, these markers are not used in clinical practice. Instead, the endogenous markers including creatinine are used to estimate GFR. However, creatinine level is not an adequate measurement of the kidney function.

Figure 1: Function of a Nephron

Moreover, the normal GFR value of most healthy people is 90 mL/min/1.73 m² or higher. However, it can be 60–89 mL/min/1.73 m² without kidney damage. The normal GFR value varies with age, sex, and body size. But, GFR between these values within more than three months along with another symptom like persisting protein in the urine indicates early kidney disease. Furthermore, the GFR is <60 mL/min/1.73 m² for more than three months indicates chronic kidney disease (CKD). More importantly, the GFR measurement is important for the diagnosis, prognosis, and treatment of kidney disease.

What is CrCl

CrCl (creatinine clearance rate) is the amount of creatinine cleared out from the blood due to the renal function. Serum creatinine is a waste product produced due to muscle movements. Kidney under normal functioning removes creatinine from the blood into the urine. Therefore, the clearance of serum creatinine becomes a measurement of kidney function. Here, the creatinine levels of both serum and urine are taken into account.

Figure 2: Creatinine

During CrCl, creatinine is collected from the urine over a given period of time, usually for 24 hours. With respect to the urine flow rate and plasma concentration of creatinine, the clearance rate of creatinine can be calculated. The normal CrCl value is 97–137 mL/min for healthy men and 88–128 mL/min is for healthy women. Also, the values of CrCl can be used to estimate GFR by using the Cockcroft-Gault formula.

Similarities Between GFR and CrCl

• GFR and CrCl are two types of measurements of the renal function.
• They measure the excretory function of the kidney.
• Also, both are important measurements for diagnosing chronic kidney disease, albuminuria, and kidney diseases.

Difference Between GFR and CrCl

Definition

GFR (glomerular filtration rate) refers to the flow rate of filtered fluid through the kidney while CrCl (creatinine clearance rate) refers to the rate at which a waste, creatinine, is “cleared” from the blood by the kidneys. Thus, this is the main difference between GFR and CrCl.

Direct or Indirect Measurements

Another difference between GFR and CrCl is that GFR is an indirect measurement while CrCl is a direct measurement.

Importance

Moreover, GFR is important for the diagnosis, prognosis, and treatment of kidney disease while CrCl is important for estimating the GFR.

Conclusion

GFR is an indirect measurement of kidney function determining the rate of filtration of fluid through the kidney. The rate of clearing creatinine of CrCl is the direct measurement of the kidney function in clinical practice, estimating the GFR. Significantly, GFR is important to measure the renal function, diagnosing kidney disease. Thus, this is the difference between GFR and CrCl. 

References:

1. FREQUENTLY ASKED QUESTIONS ABOUT GFR ESTIMATES. National Kidney Function, Available Here

Image Courtesy:

1. “Physiology of Nephron” By Madhero88 – Own workReferenceshere (CC BY 3.0) via Commons Wikimedia  
2. “Creatinine” By Jesse – Own work (CC BY-SA 3.0) via Commons Wikimedia